Recently, according to rapid increase in demands for portable electronic products, such as laptop computers, video cameras, portable phones, etc. and earnest development of electric cars, storage batteries for energy storage, robots, satellites, etc., studies of high performance secondary batteries capable of repetitive charging and discharging are actively conducted.
Currently commercialized secondary batteries are nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, lithium secondary batteries, etc. and the lithium secondary batteries thereamong are receiving attention according advantages of free charging/discharging, a very low self-discharge rate, and high energy density since a memory effect is barely generated compared to nickel-based secondary batteries.
A secondary battery is mainly used in a form of a battery pack, and various electronic devices, such as a battery management system (BMS), are embedded in the battery pack. However, such an electronic device may be exposed to an external broadcast signal or various wireless communication signals, and may malfunction due to the external broadcast signal or the various wireless communication signals. Accordingly, such an electronic device needs to be tolerant to electromagnetic waves.
FIG. 1 is a diagram schematically illustrating a charging/discharging current measuring circuit of a battery pack according to a related art.
Referring to FIG. 1, a charging/discharging current of the battery pack according to the related art is measured by measuring a voltage applied to a shunt resistor Rs and amplifying the voltage. In other words, when a potential difference is generated in the shunt resistor Rs as the charging/discharging current flows through the shunt resistor Rs , an amplifying unit 50 amplifies and outputs the potential difference to an analog to digital converter (ADC) 60. The ADC 60 changes the amplified potential difference to a digital signal. An operating unit 70 receives the digital signal, and operates the digital signal to estimate a current flowing through the shunt resistor Rs. Here, the operating unit 70 may operate the current flowing through the shunt resistor Rs considering a resistance value and an amplification gain of the shunt resistor Rs.
However, when electromagnetic waves, in particular, high frequencies, are applied from the outside, a potential difference is generated in the shunt resistor Rs as impedance of a shunt unit 40 is affected by a skin effect. Even through the potential difference generated in the shunt resistor Rs is not high, the amplifying unit 50 amplifies the potential difference. Thus, the charging/discharging current measuring circuit may misjudge that a charging/discharging current different from an actual charging/discharging current flows in the shunt resistor Rs even when a minute potential difference is generated in the shunt resistor Rs.